1. Field
The present disclosure relates generally to circuit breakers and, more particularly, the present disclosure relates to a current trip unit for a circuit breaker.
2. Description of the Related Art
Direct current fast switches serve to supervise the electrical current influx by a leader and to actuate a switch if a current threshold value is exceeded, for example, in a short circuit current. Typically, a warning is issued or the circuit is interrupted.
Conventional over-current breakers or tripping units have a magnetic yoke that surrounds a current-carrying leader. The magnetic yoke has anchors that are movable along an axis and the anchors are prevented from moving downward by a spring on the axis in a resting position. A magnetic flow through the magnetic yoke affects the anchor and forces the anchor against the resistance of the spring. If the current flowing through the leader exceeds a certain value, the magnetic force acting on the anchor is greater than the spring power of the spring. Thus, the anchor is pulled downward toward the magnetic yoke and correspondingly a trigger can be actuated to interrupt the circuit.
Conventional tripping units are bi-directional, which means that conventional units are not current direction sensitive. This conventional style of tripping is suitable in line feeder breakers. But in direct current systems there is also need to have a rectifier breaker, to protect a rectifier. A bi-directional tripping unit can not be used in a rectifier breaker to protect a rectifier. A rectifier is a current component of a circuit that allows current to pass in one direction yet blocks the flow of current in the other direction. It can be considered as a source of direct current. In fault conditions of a rectifier, a reverse current can appear in direction opposite to normal output of a rectifier. A rectifier breaker is a current component of a circuit that protects the rectifier in case of said fault of rectifier. For this reason, a conventional bi-directional unit cannot be used in a rectifier breaker, and a separate reverse current tripping device must be used with the bi-directional trip unit.
Accordingly, there is a need for a trip unit for a circuit breaker, which has the capacity to still provide circuit protection and function as a rectifier.